The data interchange format for a graphical representation of an airport on a cockpit display is specified in ARINC characteristic 816, an aviation standard that defines a database for airport moving maps. ARINC 816 defines an open encoding format for describing airport features that may be loaded in aircraft systems. Many features have a specified interchange format that consists of a series of triangle strings (i.e. an ordered list of triangles that share vertices) to compose polygons. A number of polygons collectively describes and approximates a geographic feature. The number of triangles for the accurate depiction of a feature depends upon the accuracy requirements for the map display. Typically, 1 to 2 meter resolution is required to support the lowest available range scale. For large airports covering nearly 5 nautical miles (nmi), the number of triangles required for all the airport features may be over 100,000 triangles.
Triangle decimation is a process for reducing the number of triangles needed to represent a polygon representative of a feature on a graphical display and is commonly used in gaming and medical industries such as for magnetic resonance imaging (MRI) and ultrasound displays. When the size of a polygon is close to the smallest visible element on the display (i.e. a pixel), a graphical system may render a fewer number of triangles to depict the polygonal feature.